This invention relates to electrical insulators, and in particular to insulators used in attaching heat sink assemblies comprising heat generating electronic components and heat dissipators to printed circuit boards.
In some circuit designs it is desirable to attach a plurality of such components to a single heat sink. In many heat generating components, the base or support of the component also serves as a terminal for the component. In many transistors the collector terminal is connected to a circuit through mounting hardware. The mounting hardware, is in effect, a circuit element. If a plurality of components are attached to a single heat sink, the heat sink will tend to allow current to flow directly between the components. It is therefore sometimes necessary to mount components in such a way as to:
(1) promote electrical conductivity between fasteners and components,
(2) maintaining thermal conductivity between components and the heat sink: and
(3) preventing current flow between the components and the heat sink.
Additional problems associated with unwanted current flow between components and heat sinks can also be attributed to the fact that heat sinks may have different thicknesses. Having heat sinks of various thicknesses in a single product may be the result of design interior or may be the result of manufacturing tolerances. The use of heat sinks with different thicknesses can create gaps between fastening hardware and heat sink elements, if a single type of rigid insulating hardware is used. When high voltage is present, arching can create a short between components and the heat sink or among components.
Accordingly, it is an object of the present invention to provide an electrical insulator which is able to accommodate heat sinks of various sizes.
Another object is to provide a preassembled fastener and insulator combination which facilitates assembly of heat generating electrical components to a heat sink while preventing short circuits among the components.
Yet another object is to provide an insulator which is capable of withstanding continuous clamp load between heat sinks and mounting fasteners while maintaining electrical isolation between them.
Still another object of the invention is to provide a heat sink assembly having a plurality of components which may be quickly and easily connected to a printed circuit board.
These and other objects and advantages are achieved with an insulator which is preassembled to an electrically conductive fastener. The insulator is comprised of a plastic spacer and a rubber sleeve preassembled thereto. The fastener preferably has an integral spring washer to maintain clamp load and thermal conductivity between components and an associated heat sink. In a heat sink assembly having a plurality of components, the insulators are positioned generally at the interface between the conductive fastener and the heat sink. The insulator has a collar which extends into an aperture in a heat sink. The rubber sleeve fits over the collar and extends further into the aperture. The rubber sleeve can collapse axially to accommodate heat sinks of different thicknesses. The present invention will be better understood upon reading of the following specification read in conjunction with the attached drawings.